The Buffalo Bills have signed defensive tackle Marcell Dareus, the third overall pick in the 2011 draft, to a fully guaranteed four-year, $20.4 million contract, according to a league source cited by NFL.com.

The Bills will have an option to retain him for a fifth year, according to league rules.

Marcell Dareus, the third-overall pick in this year's draft, has reached an agreement on a four-year contract with the Buffalo Bills. (AP photo)

Dareus, a 6-3, 323-pounder, will step in immediately as a starter on the Bills' three-man defensive line, the Buffalo News reported, and the team is counting on his presence to help improve the NFL's worst run defense.

Dareus was the Defensive Most Valuable Player in Alabama's victory over Texas in the January 2010 BCS national championship game.

Meantime, the rookie contracts are now falling into place, NFL.com noted, as the Broncos on Thursday signed No. 2 overall pick Von Miller and the Panthers reportedly are very close on a four-year deal with top overall pick Cam Newton.

With Dareus’ signing, 10 first-round picks have signed or agreed to terms.